Vibration energy can be used to power a variety of devices such as sensors and transmitters that are located in hard-to-reach positions in apparatus such as vehicles and machinery. Such sensors and transmitters have been conventionally hard-wired or powered by batteries, but such power sources increase the complexity of the overall apparatus or require frequent maintenance (e.g., changing or recharging of batteries).
Although devices that generate power from vibration are known in the art, such devices typically are effective at a particular resonant frequency. However, the frequency of the vibration that will be generated by a particular apparatus is not always known in advance. Therefore, it is difficult to design a power-generating device that will work over the wide range of resonant frequencies that are encountered in different apparatus.
Various approaches to overcome the resonant frequency issue have been proposed. In U.S. Patent Application Publication 2007/0125176, plural energy harvesting devices, each having a different resonant frequency, are concatenated to provide a system that can produce power of a range of frequencies.
Similarly, U.S. Pat. No. 7,667,375 uses a group of harvesters each with a single resonance mode to create a device that can operate in a range of resonant frequencies to produce power.
Other approaches are designed to operate in a rotational environment such as the inside of a tire. Each rotation of the tire creates pulses of electrical charge. This approach is shown in U.S. Patent Application Publication 2007/0063621 and U.S. Patent Application Publication 2008/0258581.
However, most of the prior art approaches feature high quality factor systems where the quality factor, Q, is defined as:Q=A/B where B is the static deformation and A is the amplitude under the resonant mode. This limits the bandwidth in which the device can produce energy.
Thus there is a need in the art for improved energy harvesting devices which can operate in a broad range of frequencies to generate power.